1. Field of the Invention
This invention relates to a photoelectric transducer switchable to a high-sensitivity or high-resolution mode.
2. Description of the Related Arts
In a photovoltaic type photoelectric transducer device which provides a high sensitivity particularly in infrared light detection, a compound semiconductor substrate having a narrow' energy band gap, such as HgCdTe (mercury-cadnium-tellurium) is doped with impurity atoms so that photodiodes are formed, with a patterned of conductive layer having a conductivity type opposite to that of the substrate. In this type of photoelectric transducer device, the photocells are integrated on a single substrate as dense as possible in order to achieve a high resolution of light detection. Accordingly, the dense integration of the photocells has caused problems of cross-talk between signals generated in adjacent photocells, resulting in a deterioration of the resolution of the image detected thereby.
In order to solve the problem, there has been proposed a structure shown in FIG. 1, in which a CdTe substrate 2 is provided with ditches 1 at a predetermined pitch, and a crystal layer 3 is formed of, for example, an epitaxial growth of p-type Hg.sub.1-x Cd.sub.x Te upon the substrate. A photodiode 5 is formed of a pn junction having an n.sup.+ layer 4 doped with an impurity of a conductivity type opposite to the conductivity type of Hg.sub.1-x Cd.sub.x Te crystal layer 3. A plurality of photodiodes 5 are formed over the portion excluding ditches 1 of substrate 2. Carriers generated by an infrared light A' input to ditch 1 are trapped in the thick portion of the Hg.sub.1-x Cd.sub.x Te crystal layer 3 in the ditch 1, on the way to reaching a nearby pn junction. The thus trapped carriers prevent crosstalk between signals detected in the adjacent photodiodes 5. However, trapping of the carriers causes deterioration of the detection sensitivity of the photodiodes.